1. Field of the Invention
The present invention relates to plasma etching systems. More specifically, the present invention relates to plasma sources used for plasma etching, chemical vapor deposition, photo-resist stripping and other applications relating to semiconductor, flat panel display, printed circuit board and other fabrication processes.
2. Description of the Related Art
Plasma and ion beam sources capable of generating uniform plasma over a wide area are needed for plasma etching, plasma enhanced chemical vapor deposition (CVD), physical vapor deposition, photoresist stripping and surface treatments for many applications. Illustrative applications include silicon and compound semiconductor fabrication, flat panel display fabrication including active matrix liquid crystal display, plasma display panels, field emission displays etc. Additional applications include hard disk drive head and media manufacturing, micro-electromechanical system manufacturing and printed wiring board fabrication.
A plasma source typically includes a radio frequency antenna, a dielectric window and a volume of gas. An electric field from an impedance matched power supply is applied to the gas by the antenna through the dielectric window. The application of the electric field to the gas generates two fields of interest with respect to plasma etching processes: a time varying electromagnetic field and a capacitive electrostatic field. The electromagnetic field strips free electrons from the gas in accordance with an inductive coupling gas plasma technique. Ions generated by the application of the electric field to the gas are utilized in accordance with a capacitive gas plasma technique. Free electrons gain energy by electric fields and generate ions by collision with neutral gases. The inductive technique is known to be more efficient in the production of ions than the capacitive coupling technique. A typical plasma etcher uses an additional electric field capacitively coupled to the substrate to increase ion energy.
Inductively coupled plasma sources using planar antennas have been mainly used for etching due to the simplicity of the antenna. High plasma density and electromagnetic wave coupling uniformity are needed for such applications. The conventional planar antenna design is generally coiled and yields narrow plasma, which has a higher power density at the center thereof, in the area where the antenna is fed. Efforts to increase the coverage area have been limited by self-resonance of the antenna. xe2x80x98Self-resonancexe2x80x99 is an electrical characteristic of the antenna due to the inductive and capacitive effects that adversely impact the performance thereof.
Hence, there is a need in the art for a system or technique for generating a high density, uniform gas plasma affording a wide coverage area.
The need in the art is addressed by the antenna of the present invention. The inventive antenna is adapted to apply a uniform electromagnetic field to a volume of gas and includes an input terminal for receiving electrical energy into the antenna and an array of radiating elements connected to the input terminal.
In the illustrative embodiment, the antenna has four radiating elements. Each radiating element includes a conductor wound in a rectangular spiral shape. Each radiating element is connected to the input terminal on one end and an output terminal on a second end thereof. The input terminal is equidistant from first, second, third and fourth output terminals connected to the first, second, third and fourth radiating elements, respectively.
The inventive antenna is adapted for use in a plasma processing system comprising a vacuum chamber, a gas disposed within the vacuum chamber, a dielectric window disposed on the vacuum chamber, and a power circuit. The power circuit includes a source of radio frequency (RF) power, a switch and an impedance matching circuit. The impedance matching circuit efficiently couples power from the RF supply to the antenna.
The inventive antenna may be inserted into the plasma without using a dielectric window, thereby enhancing power coupling efficiency. In addition, by adjusting the value of a capacitor connected to the output terminals of each radiating element, capacitive electric field components generated by the antenna can be controlled. To prevent erosion of the antenna by the plasma, the antenna may be positioned outside the vacuum chamber to induce an electric field through a dielectric plate.
The inventive antenna affords a novel method for plasma processing a device including the steps of: mounting the device within a chamber; providing a gas the chamber; and applying an electromagnetic field to the gas via an array of antenna elements disposed relative to the gas to generate a uniform distribution of the plasma.